They aren't truly property to begin with.
If they were, there would not be a limit on how long they exist under a legalized monopoly.
If you own a spoon, isn't it yours essentially forever? You have property rights to your spoon, or home, or any physical thing you own. You have the right (or at least should have the legal right) to do whatever you want with these things so long as you don't use them to harm another person. You even have property rights to yourself, since you own your own body. There are no time limits to ownership of real property.
A book itself might be property, since it is a physical thing.
A patent, however, violates your real property rights. What if you bake an apple pie according to a recipe of your own devising? You own the sugar. The flour. The shortening. The apples--and the kitchen to cook it all in. You also own your body with which you make the pie.
A patent on that recipe however, essentially says you cannot do what you have a right to do with your own things or body because someone else wrote it down and got the government to agree to enforce a monopoly on it.
And copyright is essentially a restriction of freedom of speech and the press.
All these things are not physical. They exist in the mind or on other people's property.